1. Technical Field of the Invention
The present invention relates to a method and system for providing global roaming in a cellular telecommunications system. In particular it relates to a method and system for permitting a subscriber to roam between two cellular systems configured to operate under different air interface standards or protocols.
2. Description of Related Art
There is need to provide a mobile subscriber having a single 10 telephone number and having the ability to provide access to that mobile subscriber no matter in which cellular telecommunications system that subscriber is located anywhere in the world.
While the concept of providing a global telephone number or a global roaming to a mobile terminal has been taught in U.S. Pat. No. 5,303,286 issued Apr. 12, 1994 to Robert A. Wiedeman, this patent teaches a satellite system that provides for global telephone communications. This system is not compatible with cellular telephone communications which have now been developed in various regions throughout the world.
The problem with cellular telecommunications systems operating in different regions and geographical locations is that these cellular telecommunications systems have been developed based on different air interface protocols, cell mapping configurations and user services. For example, in Europe there are common protocols referred to as "GSM" (Global System for Mobile Communications) and TACS (Total Access Communication System). Also, there are interfaces in the United States and Canada which are based on AMPS (Advanced Mobile Phone System) and D-AMPS (Digital-Advanced Mobile Phone System). Further there are standard cellular systems in Japan (Personal Digital Cellular--PDC). All of these systems operate on different air interface protocols where the messaging on the air interface is different and messaging between nodes is different. Currently, there is no system in place that allows a subscriber to have access to different cellular telecommunications systems using one subscription and one telephone number.
It is also known that different cellular service providers of the same standardized air interface protocols may allow subscribers to roam between these different cellular telecommunications service providers. This roaming feature however is for a mobile subscriber who subscribes to one form of cellular telecommunications systems protocol and not for a subscriber wishing to roam in normally non-compatible cellular systems.
A method of global roaming between non-compatible interfaces is disclosed in U.S. Ser. No. 08/530,161 filed Sep. 29, 1995 assigned to the same assignee as the present invention, i.e. Telefonaktiebolaget L M Ericsson, and titled "A method and arrangement relating to telecommunications systems". In this application, there is disclosed the introduction of an international telecommunications system including an international home location register (HLR) and an international mobile switching center (MSC). The international system is connected through appropriate interfaces to a home system and a guest system. In order to be able to register in the guest system it is required that the subscriber is to subscribe to both the international system and the home system. While this system allows for global roaming between non-compatible air interfaces, it introduces an extra management layer to be operated by an "international" operator.
Accordingly, there is a need to provide a global roaming service to a subscriber to allow the subscriber to roam between non-compatible cellular telecommunications systems without the introduction of extra layers of network management.